Power modulation of a thermal generator

ABSTRACT

A process for modulating the power of a gas turbine by variation of the inlet temperature of the working fluid in a compressor located upstream of a turbine. The compressor and turbine are each staged and the working fluid is cooled at least before the last compressor stage by gasification of a liquefied gas. A portion of the cooling energy produced by expansion of the liquefied gas can be returned to the liquefied gas in storage to cool the latter.

United States Patent [191 Waeselynck 1 Feb. 25, 1975 POWER MODULATION OFA THERMAL GENERATOR [75] Inventor: Raymond Francois Maurice Waeselynck,Paris, France [73] Assignee: Compagnie Francaise de Raffinage,

Paris, France [22] Filed: Nov. 14, 1972 [21] Appl. No.: 306,557

[30] Foreign Application Priority Data Nov. 22, 1971 France 71.41723[52] US. Cl 60/39.03, 60/3917, 60/39.46, 60/652, 62/52 [51] Int. Cl.F02c 9/14 [58] Field of Search 60/3902, 39.03, 39.18 R, 60/3918 B, 36,39.71, 39.12, 39.46, 39.17; 62/52, 53

[56] References Cited UNITED STATES PATENTS Bridgeman 60/3946 2,988,8846/1961 Poyit 60/3917 3,154,928 11/1964 Harmens... 60/36 3,631,673 1/1972Charrier.... 60/3902 3,720,057 3/1973 Arensen.... 60/3902 3,726,1014/1973 Arenson 60/3946 Primary ExaminerWilliam L. Freeh AssistantExaminerWarren Olsen [57] ABSTRACT A process for modulating the power ofa gas turbine by variation of the inlet temperature of the working fluidin a compressor located upstream of a turbine. The compressor andturbine are each staged and the working fluid is cooled at least beforethe last compressor stage by gasification of a liquefied gas. A portionof the cooling energy produced by expansion of the liquefied gas can bereturned to the liquefied gas in storage to cool the latter.

9 Claims, 5 Drawing Figures PATENIEU FEB2 5 i975 SHEET 10F 11 PATENTEDFEB 2 5 I875 SHEEI 2 OF 4 PATENTEU FEB 2 5 i975 SHEET U BF 4 POWERMODULATION OF A THERMAL GENERATOR BRIEF SUMMARY OF THE INVENTION Thisinvention relates to a process for increasing the efficiency of thermalgenerators, particularly for modulating their power by use ofrefrigeration, and to the application of this process, for example, forindirect electrical power storage.

The advantage of increasing the power of a thermal generator of a givensize and of increasing its efficiency are obvious in themselves and neednot be explained. As for electrical power storage, it is known thatelectrical power consumption varies on the one hand according to theseason of the year, and on the other hand according to the time of day,but power production must closely follow consumption due to theinability to store electricity. This requirement causes substantialeconomic loss as it entails long periods of reduced output since thesize of the generating installations must correspond to the highestpower demand while such a demand need be actually satisfied only duringa fraction of the operating time.

Indirect electrical power storage installations have already beenrealized in the use of artificial lakes in which pumps raise waterduring non-peak hours, but these gravitational storage installations arefar from satisfactory, and are only possible in selected geographicalsites.

The invention is based upon the known fact that lowering the temperatureof the cold source of a thermal machine increases its thermodynamicefficiency and increases the power obtained per unit, weight or volumeof the working fluid. For instance, when the working fluid is a noncondensible gas, by lowering the temperature of the cold source, thedensity of the gas going through the cycle increases and consequentlyincreases the power produced per unit volume of the working fluid. 5

An object of the invention is to provide a process in which the above isutilized in order to increase power production from a given thermalmachine and/or to allow utilization of a smaller thermal machine toobtain a given power. In other words, the invention seeks to increasethe gross power of thermal machines of a given size, as well as toimprove their utilization and particularly to increase their efficiency.

The invention contemplates a process in which the output power ofthermal machines can be modulated by refrigeration. The application ofthis process permits a more complete and more continuous use of thepower of a thermal power generator, as well as a modulation of the poweroutput of a thermal machine without changing, at least within widelimits, the speed of the machine, nor the maximum temperature in theoperating cycle.

According to the invention, it is not necessary to produce therefrigeration effect near the thermal machine. The refrigerationmachines may therefore be located in any place. particularly in a placewhere, due to production. utilization or storage of a product, thecooling effect is transferred to this product. This product may undergo,total or partial, transformation, and be stored near the thermalmachine.

Liquefied gases are specific substances for storage of refrigerationeffect and more particularly liquefied natural gases, liquefiedpetroleum gases and liquefied gases from the air. Liquefaction of thesegases is effected to facilitate their storage and transportation,theymust be re-gasified before use. This re-gasification produces alarge quantity of cooling energy hereafter called frigories which may beused in numerous applications, and particularly in power production.Methane is an example of a gas which is liquefied, transported by ship,stored in depots, then re-gasified under pressure and distributedthrough pipe lines over great distances.

An object of the present invention is the specific implementation,giving a maximum efficiency to the utilization of the frigoriescontained in liquefied gas and permitting continuously ordiscontinuously to obtain high power and high efficiency in powergeneration by means of a gas turbine.

The thermal machine described above effects compression, then expansionof the working fluid.

The Applicant has established that it is advantageous to perform thefluid compression in several stages and to cool the working fluidbetween stages. Additionally, it is also advantageous to perform theexpansion of the working fluid in several stages.

A further object of the invention is to provide a process for themodulation of gas turbine power production by variation of the inlettemperature of the working fluid in a compression device located aheadof the gas turbine inlet, said process being characterized in that theworking fluid compression and subsequent expansion are performed inseveral stages, each compression stage following a cooling of theworking fluid by means of the cold effect produced during the gasifyingof a liquefied gas in a container connected on the one hand to theliquefied gas storage tank and on the other hand to a compressor.

The invention will be described hereafter in relation to an apparatusand method comprising two compression stages and two expansion stages.

It is necessary to dry to a maximum the inlet air in order to avoid aquick frosting of the low temperature coolers. This the reason why,before each stage of air cooling by means of the cooling fluid (aliquefied gas), the air is first cooled by a coolant consisting of waterand anti-freeze. The air later goes through a separator of waterdroplets; the remaining water in the air will be frozen in the maincooler as very small particles which will be carried along by the airand will not lie in the main cooler as a film.

The first compressor preferably operates at a rather low compressionratio to serve the part of a supercharging device fulfilling twofunctions:

by variation of its speed, it permits adaptation of the entire circuitto the conditions of optimum efficiency when the air temperature varies;

by multiplying the air pressure by the compression ratio, it permitsreduction of the surface area of the cooler located downstream.

BRIEF DESCRIPTION OF THE DRAWING The following description will be madewith reference to the appended drawings in which:

FIG. 1 diagrammatically illustrates a circuit for effecting the processaccording to the invention by means of a utilization device for the coldeffect which is producted;

FIG. 2 shows another similar circuit according to the invention;

FIG. 3 shows a device for utilization of the cooling effect by coolingthe liquefied gas and this device can be added to the utilizationdevices shown in FIGS. 1 and 2;

FIG. 4 diagrammatically shows another arrangement according to theinvention for utilization of the cooling effect by cooling the liquefiedgas stock; and

FIG. 5 shows a supplementary refrigeration generation devicr whosecooling effect is used to cool at least a portion of the liquefied gasstock and this device may be added to the utilization devicesrepresented in FIGS. 1 and 2.

DETAILED DESCRIPTION The various figures are simplified in that they donot include auxiliary equipment such as pumps, etc., the necessity andthe use of which are obvious to those skilled in the art.

With reference to the apparatus of FIG. 1, therein is not contemplatedany cooling of the liquefied storage gas.

Air is introduced through line 1 into a scrubber 2 into which a coolantconsisting of water with added antifreeze is sprayed by nozzle device 3.The air is thus cooled to a temperature between 2C. and +2C., at whichtemperature the greatest part of the water present in the air iscondensed.

The coolant is introduced into the scrubber 2 through a line 4 at atemperature between -5C. and l 0C., this temperature being obtained bypassing the coolant, collected by line 5, through an exchanger 6supplied with a refrigerating fluid through circuit or loop 7 connectedto the outlet and of a gasification device of a liquefied gas.

In the upper part of scrubber 2, a cyclone 8 separates any remainingtraces of water droplets from the air.

The air from scrubber 2 is introduced, at a temperature between 2C. and+2C, through line 9 into a compressor C1. The compressed air isintroduced through a line 10 into a cold water cooler 11 in which watercirculates through a line 12. Then, the air is introduced through line13 into a scrubber 2' which operates similar to the scrubber 2 exceptthat it is fed with air under pressure at a temperature in theneighborhood of 30C. Reference characters 3', 5' and 8in the scrubber 2'designate structure corresponding to 3, 5 and 8 in the scrubber 2. Inthe scrubber 2' the air is substantially dried.

The dried air is discharged from scrubber 2' at a temperature between 2Cand +2C and is introduced through lines 14 into a main cooler 15.Liquefied gas enters the main cooler through a line 16 and exits via aline 17 and serves as the refrigeration fluid in cooler 15. The coldenergy in the liquefied gas is thus utilized to cool the air fed tocompressor C and this increases the efficiency of the compressor andlowers the load on the turbines hence increasing the available output.The air is fed from cooler at very low temperature to compressor C whereit is compressed and then is passed to a heat recovery device 18 byopening valve l9 and closing valve 20. The air is heated in recoverydevice 18 and then passes to a combustion chamber 21 through valve 22which is opened. A fuel is introduced into the chamber 21 through line23. The resulting combustion gas from chamber 21 is passed to a turbineT, through line 24. After a first stage, a part of the heat content inthe gas is recovered by passing the exhaust gas from T into the heatrecovery device 18 (valve 25 being opened and valve 26 being closed).The gas, after having given up heat in device 18 is admitted intoturbine T through line 27 (valve 28 being opened) and exhaust iseffected through line 30 at atmospheric pressure.

The liquefied gas 31, stored in tank 32, is pumped to the main cooler 15through line 16. The gas discharged from line 17 is supplied either toother gasifiers or to utilization devices or the gas pipelines.

With reference to FIG. 2 which represents another embodiment of theprocess according to the invention employing a device for theutilization of the refrigeration effect, this embodiment as in FIG. Idoes not include a cooling of the liquefied gas stock.

In the embodiment of FIG. 2, air is introduced through line 1 intoscrubber 2 similar to the scrubber described in FIG. 1, and referencecharacters 2-8 in FIG. 2 designate the same parts as in FIG. 1.

The air in line 50 at a temperature which is between 2C and +2C, isintroduced into first main cooler 51. The liquefied gas refrigerationfluid is fed from tank 32 through line 16 to cooler 51. The cooled airfrom cooler 51 is introduced into compressor C1. The compressed air inline 54 passes into second main cooler 55, the refrigerating fluid ofwhich is liquefied gas coming from tank 32 through line 16. The air indischarge line 58 from cooler 55 is fed to compressor C2 where it isfurther compressed to a maximum value. Turbines T and T are fed, as inFIG. 1, from the air compressed to a maximum coming from compressor C2.

The gas coming from the main coolers 51 and 55 is fed through line 17 toother gasifiers or to consumption devices.

The implementation of the process of the invention is accompanied by animportant cooling of the air admitted into compressor C2 or intocompressors C1 and C2, and this enables a high expansion ratio with ahigh efficiency and consequently allows installation of the heatrecovery device 18 between turbines T, and T Nevertheless, the twoembodiments which have just been described, need not include heatrecovery device 18 in which case the compressed air from compressor C2is then directly introduced into the combustion chamber 21 (valve 20being opened, and valves 19 and 22 being closed). Furthermore, theexhaust gas from turbine T is directly admitted into turbine T (valves26 being opened). It is also possible to place the recuperating devicenot between T and T but after T nevertheless, the increase incompression ratio and efficiency which the invention allows to obtain,affords the possibility of placing the heat recovery device after T,, inwhich case it is less heavy and less bulky than if it were placed afterT without loss and even with a slight gain in efficiency.

The magnitude of flow of the liquefied gas into the main coolers ofFIGS. 1 and 2 depends upon the gas demand, and therefore it is notlinked to the operating parameters of the process of the invention.Nevertheless, this may be the case when the liquefied gas is methane andgenerally, a natural gas whose peaks of consumption correspond to theconsumption peaks of the power produced by the thermal machine. Besides,it is usual in gasifyin g centers to maintain the flow of liquefied gasmore or less constant independently of the gas consumption by using gasstorage means such as natural underground reservoirs, gasholders, verylong pipelines under high pressure, etc. The power produced is then thatof a basic power plant.

It is possible to accept variations in the supply of liquefied gas inthe main coolers as long as these variations are not too sudden, as theycould then entail damage to the compressors.

Another embodiment of the process according to the present invention,contemplates cooling the liquefied gas stock or a part thereof. Threeconfigurations thereof have been represented in FIGS. 3, 4 and 5.

FIG. 3 shows a configuration which can be used instead of tank 32 ofFIGS. 1 and 2 and is additive to the utilization arrangementsrepresented in FIGS. 1 and 2. The cooled liquid can be mixed in variableproportions with non-cooled liquid before being introduced into the aircoolers. The supplementary refrigeration'effect pro duced by the coolingof the liquefied gas stock is stored in the container used for liquefiedgas storage.

Next shall be described the configuration and its operation. Tosimplify, there will be distinguished two extreme cases of operation,one during off peak hours (during which supplementary refrigerationeffect is stored), the other during peak hours (during which the storedsupplementary refrigeration effect is consumed).

During off peak hours:

A flow of liquefied gas coming from the outlet 60 of tank 61 (valve 62being opened) is expanded in the evaporator 63. The very cold liquefiedgas collected in line 64 is introduced into the lower part of tank 61through line 65 (valve 66 being opened and valve 67 being closed). Thecooled liquefied gas introduced through a lower opening 68 is preventedfrom mixing with non-cooled liquefied gas by the presence of partitionmeans, e.g., cylindrical vertical partition 69 in tank 61.

The flow of liquefied gas to be gasified is withdrawn from tank 61through the outlet 70. Valve 71 is opened and liquefied gas flowsthrough line 72 to a condenser 73 (valve 77 being opened) whichcondenses the gas compressed in C3 (valves 74 and 75 being opened).After condensing, this gas is introduced into the flow of liquefied gasin line 72 (valve 76 being opened). From the outlet of condenser 73 theliquefied gas is passed through line 16 to the main cooler (FIG. 1) orto the main coolers 51 and 55 (FIG. 2).

During peak hours:

Compressor C3 does not operate, valves 62, 74, 75, 66, 71, 76 and 77 areclosed, valve 67 is opened, so that the flow of liquefied gas to begasified totally comes from the opening 68 of tank 61 and is thereforevery cold. Condenser 73 is by-passed during peak hours by line 78.

The two types of operation which have just been described are extremecases, but they are not the only ones: thus, during non-peak hours,valve 67 may be partially opened, conversely, during peak hours, valve71 is generally opened, and additionally, compressor C3 may be operated.

With reference to FIG. 4 which represents a configuration for utilizingrefrigeration effect including means for generating supplementaryrefrigeration effect from the cooling of at least a part of theliquefied gas stock, the cooled liquid first of all, passing through aspecial cooler before being mixed with the remainder of the liquidintroduced into the air coolers. The cooling effect produced by thecooling of the liquefied gas stock is stored in the liquefied gasstorage container. This configuration may be used instead of the systemconstituted by the tank 32 and the main coolers 51 and 55 represented inFIG. 2.

This configuration and its operation will next be described for thecases of operation during off peak hours and during peak hours.

During off peak hours:

Operation is very similar to that described with reference to FIG. 3.Valves 62, 74, 75, 76, 77 and 67 are opened, compressor C3 is inoperation, the cooled liquefied gas coming from evaporator 63 isre-introduced into the tank 61 through the lower opening 68. Valves 79and 80 are closed. The main coolers 55 and 51 are supplied withliquefied gas through line 16. The gas coming out of the main coolers S1and 55 is supplied through line 17 to other gasifiers or to consumptionmeans.

During peak hours:

Compressor C3 is not in operation, valves 62, 74, 75, 76, 77 and 67 areclosed. Valves 79 and 80 are opened. The cooled liquefied gas isintroduced into a special cooler 82 through line 83, and it isdischarged through line 84 after heat exchange with the air coming fromthe main cooler 51. The main coolers 55 and 51 are supplied withliquefied gas through line 16, the condenser 73 is by-passed by line 78.

The modes of operation which have just been de scribed are extreme casesand others are possible, e.g., during off peak hours valves 79 and 80may be partially opened. I

With reference to FIG. 5 which represents a configuration for thegeneration of supplementary cooling effect from the cooling of at leasta portion of the liquefied gas stock, this configuration may be added tothe configuration of the utilization of refrigeration effect representedin' FIGS. 1 and 2. The supplementary refrigerating effect produced bycooling of the liquefied gas stock is stored separately from that usedfor liquefied gas storage. The cooled liquid may be either mixed invariable proportions with the non-cooled liquid before being introducedinto the air coolers, or first introducted into the air cooler.

Next shall be described the configuration and its operation in twoextreme cases:

During off peak hours:

Valves 85, 86, 87, 88 and 89 are opened, compressor C3 is operated. Theliquefied gas coming from tank 32 and passing through valve is expandedin the evaporator 90, a large refrigeration effect is generated duringthis expansion which is stored in the evaporator 90 and is not used. Thecompressed gas coming from C3 is condensed in the condenser 73, throughwhich passes the flow of liquefied gas coming from tank 32 through lines91 and 92. The liquefied gas is then fed through line 16 to the maincooler (reference character 15 in FIG. 1) or to the main coolers(reference characters 51 and 55 in FIG. 2).

During peak hours:

Valves 85, 86, 87, 88 and 89 are closed, compressor C3 is stopped.

Distinction must be made as to whether the configuration includesspecial cooler 82 or not.

When the configuration includes special cooler 82, it can replace thesystem in FIG. 4 including the special cooler 82, the tank 61 and theevaporator 63. The line with valve 93 is omitted, valves 94 and 95 areopened.

The special cooler 82 is supplied with cooled liquefied gas through line96 to cool the air coming from the main cooler 51. The resulting verylow temperature air is then introduced into compressor C1.

The liquefied gas is then introduced into the main cooler 55 throughline 16 via lines 97, 92 and 78 (condenser 73 is by-passed by line 78).

When the configuration is not provided with a special cooler 82, it canreplace the system including the tank 61 and the evaporator 63represented in FIG. 3. The line including valve 93 exists. Lines 96 and97 as well as valves 94 and 95 are omitted. Valve 93 is opened, thecooled liquefied gas directly joins the liquefied gas coming from tank32 through line 91.

The following examples which are given are not limitative, they relateto the use of methane as the liquefied gas. Examples I and II relate tothe implementations of the process respectively represented in FIGS. 1and 2. Example III relates .to the configuration represented in FIG. 3for the implementation of the process in FIG. 1. The numerical data usedin the example are as follows:

the compression of air:

Average compressor adiabatic efficiency (adopted for the simplification)0.83

Ambient air temperature 290 K For air temperature rise C= 0.26

Gas turbine inlet temperature: 1,173K

Gas expansion C 0.26 C/C 0.265

This example relates to FIG. I.

A. In the absence of exchanger (18) COMPRESSION: Air admitted at 2C(i.e., 275K) total compression ratio 34 First compression body (C1)compression ratio 2.5 Compression work I T 0.246 X 94.5 calories Airtemperature after compression:

Second compression body (C2) compression ratio Air temperature at theinlet after cooling 173K Compression work:

Tllc [(13 7)0-28 T" 0.246 X 223.5 calories Air Temperature aftercompression:

Total compression work: T T T" =0.426 X 318 calories, 78.5 calories AIRTEMPERATURE RISE Q 0.26 (1173 396.5) 0.26 X 776.5 calories 202 caloriesEXPANSION: Total expansion ratio:

Gas temperature after expansion 1173 490 683K Second expansion body (TExpansion ratio Expansion work T",= 1.015 X 0.26 X 0.85 X 683 [11/(2.5)-

1.015 X 0.26 X 124.5 calories Gas temperature after expansion Totalexpansion work T, T, T", 1.015 X 0.246 X (490 +124.5)= 1.015 X 0.246 X614.5 calories 162.5 calories USEFUL WORK:

T T, T 162.5 78.5 84 calories per kilog of air EFFICIENCY p T,,/Q824/202 0.408 B. In the presence of the exchanger (18) RECUPERATOR: Gastemperature before recuperator 18 and before second expansion in T 683KAir temperature after compression: 396.5K Gas temperature drop in theexchanger:

Heat recovery calories:

143.5 X 0.26 37.5 calories Necessary heat for air temperature rise 20237.5 164.5 calories SECOND EXPANSION Temperature after exchangerExpansion work T, 1.015 X 0.26 X 0.85 X 549.5 [I -1/(2.5)-

T",= 1.015 X 0.26 X100 Total expansion work T,= 1.015 X 0.26 (490 155.9calories USEFUL WORK T (155.9 78.5) 0.98

T 77.4 X 0.98 75.8 calories per kilog of air 0 EFFICIENCY p 75.8/161.50.46

EXAMPLE II This example relates to FIG. 2.

A. In the absence of the recuperator l8 COMPRESSION Air admitted at 100C(i.e., 173K) Total compression ratio 35 First body (Cl) compressionratio 2.5

Compression work T 0.246 X 173/0.83 [(2.5)"' -l 0.246 X 60.5

Air temperature after compression:

Second body (C2) compression ratio: 35/2.5 14

Air temperature on inlet after cooling: 173K Compression work:

T" 0.246 X 173/0.83 X [(14)"' -1 0.246 X Air temperature aftercompression: 173 225 Total compression work:

T 0.246 (60.5 225) 70.1 calories AIR TEMPERATURE RISE:

Q 0.26 (1173 398) 0.26 X 775 202 calories EXPANSION:

Total expansion ratio: 35/108 32.3

First body T expansion ratio: 32.3/2.5 12.9

Expansion work:

T, 1.015 X 0.26 X 0.85 X 1173 [ll/(12.9)'

Gas temperature after expansion Second body (T expansion ratio: 2.5

Expansion work:

T",=1.015 X 0.26 X 681 [1- l/(2.5)' 1.015

X 0.26 X 124 calories Gas temperature after expansion: 681 124 557KTotal expansion work:

T,= 1.015 X0.26 (492 124) 1.015 X 0.26 X 616 T, 163 calories USEFULWORK:

T (T, T 0.96 (163 70.1) 0.98 91 calories per kilog of air EFFICIENCY:91/202 0.45

B. In the presence of the recuperator l8 RECUPERATOR: Gas temperaturebefore recuperation and before second expansion in T 681K Airtemperature after compression: 398K Gas temperature drop in theexchanger:

Recovery of heat in calories:

141.5 X 0.26 37 calories Necessary heat for air temperature rise:

202 37 165 calories SECOND EXPANSION: Gas temperature afterrecuperation:

EXAMPLE III The air temperature at the inlet of the first compressorbody, which in the case of Example I in the absence of the recuperator18, was equal to 275K, is lowered by 40C and is equal to 233K duringoperation in peak hours. Let us assume for the time being that theopening of the gas turbine circuit is not modified, nor is therevolution speed of the two compression devices.

On the one hand, the density of the inlet air is increased according tothe ratio of the absolute temperatures 275/233.

On the other hand, the compression ratio of the first body rises from2.5 to l lP so that:

without change in the compression work per kilog of air as opening andspeed remain constant. We deduce therefrom:

P lP 2.87 and the pressure at the gas turbine inlet goes from 31.7 X Pto 31.7 P X 2.87/2.5 36.4

To enable this new flow of gas to pass into the turbine, it would benecessary to increase the pressure at the inlet by the ratio 275/233'=1.18 and not by the ratio 2.87/25 1.147. This adaptation requires thatthe speed of the first compression body be increased by the ratio V1.18/1.147, that is to say about 1.5 percent. The expansion ratio isthen increased by the ratio 1.18 as air densities.

For the remainder of the calculations, we shall neglect this slightadaptation which would only improve the useful work ratio per kilog ofair.

If, therefore, we do not change the speed nor the opening, the totalcompression work is not modified and remains equal to 78.5 calories. Theexpansion work is slightly increased and the useful work per kilog ofair goes from 84 to 85.9 calories.

The total useful work is thus increased in the ratio 85.9/84 multipliedby the ratio in weight of air flows, that is to say, finally, in theratio:

The peak power is thus increased by 21 percent.

Efficiency is itself improved in the ratio 85.9/84 and goes from 0.408to 0.408 X 85.9/84 0.416.

It would of course be possible to lower the air temperature below 40C atthe inlet of the first compression body by increasing the refrigeratingmachine power. The available power during peak hours would thus beincreased.

What is claimed is:

l. A process for modulating the power of a gas turbine by variation ofthe inlet temperature of the working fluid in a compressor locatedupstream of the gas turbine, said process comprising forming thecompression and turbine steps each in a plurality of stages, cooling theworking fluid before at least the last compression stage by heatexchange with liquified gas stored in a tank, producing a furtherrefrigeration of the liquified gas stored in said tank by supplying atleast a part of the liquefied gas during off-peak hours from said tankto an evaporator wherefrom are obtained a gas fraction at the top and acooled liquefied gas fraction at the bottom, compressing the gasfraction produced in said evaporator, then condensing the thuscompressed gas fraction by effecting heat exchange thereof with a flowof liquefied gas coming from said tank and going to cool the workingfluid and introducing the now condensed gas fraction into said flow ofliquefied gas coming from said tank and going to cool the working fluid,storing the cooled liquefied gas fraction collected in said evaporatorduring offpeak hours and utilizing the same during peak hours togetherwith the liquefied gas from said tank to cool the working fluid.

2. A process as claimed in claim 1, in which the cooled liquefied gasfraction collected in said evaporator is stored during off-peak hours inthe same tank used for storing the liquefied gas by partitioning thetank to prevent mixing of the cooled liquefied gas fraction with thenon-cooled liquefied gas.

3. A process as claimed in claim 1, in which the cooled liquefied gasfraction collected in asid evaporator is stored during off-peak hoursseparately from the tank used for the non-cooled liquefied gas.

4. A process as claimed in claim 1 wherein the compression of theworking fluid is effected in two stages, the process further comprisingremoving water from the working fluid before introduction into the firstcompressor stage by cooling said fluid by spraying at a temperaturelower than C with a mixture of water and anti-freeze and thensubsequently separating the condensed water from the working fluid.

5. A process as claimed in claim 4 wherein the working fluid coming outof the first compressor stage is passed through a first cooler, thenthrough a container where it is freed from traces of water vapor byspraying, at a temperature lower than 0C, with a mixture of water andanti-freeze and subsequently separating the condensed water from theworking fluid and finally passing the working fluid through a second,main cooler from which it is discharged at a temperature of about l00Cbefore being admitted into the second compressor stage.

6. A process as claimed in claim 1 wherein the compression of theworking fluid is effected in two stages, the working fluid being passedbefore being introduced into the first compressor stage through acontainer where it is freed from water vapor by cooling said fluid byspraying the same at a temperature lower than 0C, with a mixture ofwater and anti-freeze and subsequently separating the condensed waterfrom the working fluid, then passing the working fluid through a maincooler from which it is discharged at a temperature of about -l00C to beadmitted into the first compressor stage.

7. A process as claimed in claim 6 wherein the working fluid coming fromthe first compressor stage is passed through a second main cooler fromwhich it is discharged at a temperature of about C before being admittedto the second compressor stage.

8. A process as claimed in claim 1 wherein the working fluid compressedin two stages, wherein the first compressor stage operates at arelatively low compression ratio of about 2.5 and the second compressorstage compresses the fluid to a higher value therethan.

9. A process as claimed in claim 1 wherein the lique-

1. A process for modulating the power of a gas turbine by variation ofthe inlet temperature of the working fluid in a compressor locatedupstream of the gas turbine, said process comprising forming thecompression and turbine steps each in a plurality of stages, cooling theworking fluid before at least the last compression stage by heatexchange with liquified gas stored in a tank, producing a furtherrefrigeration of the liquified gas stored in said tank by supplying atleast a part of the liquefied gas during off-peak hours from said tankto an evaporator wherefrom are obtained a gas fraction at the top and acooled liquefied gas fraction at the bottom, compressing the gasfraction produced in said evaporator, then condensing the thuscompressed gas fraction by effecting heat exchange thereof with a flowof liquefied gas coming from said tank and going to cool the workingfluid and introducing the now condensed gas fraction into said flow ofliquefied gas coming from said tank and going to cool the working fluid,storing the cooled liquefied gas fraction collected in said evaporatorduring off-peak hours and utilizing the same during peak hours togetherwith the liquefied gas from said tank to cool the working fluid.
 2. Aprocess as claimed in claim 1, in which the cooled liquefied gasfraction collected in said evaporator is stored during off-peak hours inthe same tank used for storing the liquefied gas by partitioning thetank to prevent mixing of the cooled liquefied gas fraction with thenon-cooled liquefied gas.
 3. A process as claimed in claim 1, in whichthe cooled liquefied gas fraction collected in asid evaporator is storedduring off-peak hours separately from the tank used for the non-cooledliquefied gas.
 4. A process as claimed in claim 1 wherein thecompression of the working fluid is effected in two stages, the processfurther comprising removing water from the working fluid beforeintroduction into the first compressor stage by cooling said fluid byspraying at a temperature lower than 0*C with a mixture of water andanti-freeze and then subsequently separating the condensed water fromthe working fluid.
 5. A process as claimed in claim 4 wherein theworking fluid coming out of the first compressor stage is passed througha first cooler, then through a container where it is freed from tracesof water vapor by spraying, at a temperature lower than 0*C, with amixture of water and anti-freeze and subsequently separating thecondensed water from the working fluid and finally passing the workingfluid through a second, main cooler from which it is discharged at atemperature of about -100*C before being admitted into the secondcompressor stage.
 6. A process as claimed in claim 1 wherein thecompression of the working fluid is effected in two stages, the workingfluid being passed before being introduced into the first compressorstage through a container where it is freed from water vapor by coolingsaid fluid by spraying the same at a temperature lower than 0*C, with amixture of water and anTi-freeze and subsequently separating thecondensed water from the working fluid, then passing the working fluidthrough a main cooler from which it is discharged at a temperature ofabout -100*C to be admitted into the first compressor stage.
 7. Aprocess as claimed in claim 6 wherein the working fluid coming from thefirst compressor stage is passed through a second main cooler from whichit is discharged at a temperature of about -100*C before being admittedto the second compressor stage.
 8. A process as claimed in claim 1wherein the working fluid compressed in two stages, wherein the firstcompressor stage operates at a relatively low compression ratio of about2.5 and the second compressor stage compresses the fluid to a highervalue therethan.
 9. A process as claimed in claim 1 wherein theliquefied gas is methane.